I built in some robust animation and targeting for the cannons on the large destroyer ship. This works quite and looks great, however, I seem to have developed the gamedev equivalent of writer's block and can't decide what kind of ordinance they should shoot!

While I could just regurgitate one of the existing weapons in my game (laser, plasma, rockets), I think it's about time to introduce something new... but I can't figure out what. These guns are some pretty big cannons. What do you think they should shoot?

Not sure if this helps, but I'm currently leaning towards a plot something along the lines of the player is a space privateer on a mission to disable and steal something from the mile-long imperial destroyer (the big ship with the cannons), but comes only to find it's already under attack by an alien force.

Additionally, part of the conundrum is since these guns are huge (the barrel is bigger than the player ship) presumably they must shoot something pretty powerful, likely meaning instant death if they shoot the player. In that case, can they be easily avoided like the easily dodgable, but powerful rockets that some of the smaller ships shoot? Do they take a long time between shots? Or do they simply not target the player most of the time? Maybe they just focus on the aliens?

Perhaps another annoyance with these cannons is if the player gets too close the barrel will swing around and smack the player ship. Think it should stop trying to target the player if you get too close? Or is it more realistic that the enemy using the cannon *would* try to smack the player with the cannon if you get too close?

Here's a screenshot of a battery of 3 of the cannons I'm talking about (there are 22 total, they are destructible):

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Interesting thought after putting this into print: I could go the route that the cannons are powerful, but don't target the player. This level is already extremely hard, perhaps the best solution is that the player whose real goal is to pirate the ship turns out to be the unlikely hero and in fact saves the ship... and after being celebrated as a hero takes advantage of his newfound respect and plunders his goal anyway. Another benefit of this approach is it provides a time-incentive for the player to demolish the enemies quickly, for if he doesn't the cannons will be destroyed by the alien forces early on and won't still be around to protect the player from some of the harder parts later. Also would allow for some fun strategies in drawing enemies into the line of cannon fire.

That still doesn't solve the challenge of what ordinance these cannons should use, however.

A good explanation why the cannons aren't tracking the player's ship would be that they're planet killers (or city killers) that you use to bombard cities or entire continents from space, not engineered to target anything smaller than a kilometer.

They could be shooting micro black hole bombs. These destroy large ships / entire continents / planets by generating (via some unspecified sci-fi technology) an artificial black hole that exists for 1-2 milliseconds. The massive gravitation during that short time tears apart everything within some hundreds of kilometers in an implosion-shockwave-like manner, without actually sucking everything into the black hole. This might in fact even work as an "area of effect" weapon against smaller ships too, if there is a logic inside the bomb to make it go off at a certain distance after being fired.

Drilling torpedoes would be another fun thing for a huge cannon, such as the thing they used to sink the battleship in "Tomorrow Never Dies". Except of course you can fire it in space, and it's propelled with some kind of rocket motor.

Chaff cannons, both as missle countermeasure and as an area denial weapon would be another idea. Basically when the enemy fires 10-20 missles at you, the chaff cannons fire some large amount of chaff (say, 100 kilograms of scrap metal, or whatever is in this big ship's waste dump) which will inevitably collide with the incoming rockets, causing them to explode prematurely or malfunction. Such a kind of cannon would have to be big to be effective.

I think they should shoot ninjas.